Electron-discharge device



Jan. 1, 1957 R. ADLER 2,776,388

ELECTRON-DISCHARGE DEVICE Filed May 11, 1953 ROBERT ADLER INVENTOR.

,l-ns ATTORNEY.-

United States Patent ELECTRON-DISCHARGE DEVICE Robert Adler, Northfield,Ill., assignor to Zenith Radio Corporation, a corporation of IllinoisApplication May 11, 1953, Serial No. 354,171

Claims. (0 313-72) This invention relates to electron-discharge devicesand more particularly to such devices of the beam deflection type.

The advantages of beam deflection tubes for certain applications havelong been known in the art. For example, such tubes are inherently welladapted for balanced operation and are particularly well suited forapplications in which direct-current coupling is required. However, beamdeflection tubes have not been extensively used because of severalconsiderations with respect to which grid-controlled tubes havepresented superior operating characteristics. Specifically,grid-controlled tubes have generally been considered capable ofproviding materially greater space current than beam deflection tubes,although this limitation has largely been overcome by the provision ofsheet-beam deflection tubes. It has also been possible to achievematerially greater transconductances with grid control than withelectrostatic deflection; however, there are many applications in whichthe characteristically lower transconductance of beam deflection tubesis not to be considered a disadvantage.

In spite of the progress which has been made in the development of beamdeflection tubes, optimum utilization of their desirable characteristicshas not been achieved. In particular, the advantage of inherentadaptation to balanced operation is largely counterbalanced by atendency to draw excessive beam current to the deflectors in response tothe application of large signal voltages, thus undesirably loading theinput circuit. This tendency may be reduced by increasing the spacingbetween the deflectors, but this compromise is accompanied by a decreasein the already relatively low transconductance of the input system.Moreover, the deflector bias required to focus the beam on the outputelectrode system is also decreased as the deflector spacing isincreased, with the result that direct-current coupling to thepositively biased output electrodes of the preceding stage is no longerfeasible.

. It is, therefore a primary object of the present invention to providea new and improved beam deflection tube in which stable transconductanceis achieved over a wide range of positive bias potentials applied to theinput deflectors.

It is a further object'of the invention to provide a new and improvedbeam deflection tube capable of accommodating relatively large inputsignal voltages without drawing excessive deflector current, and toachieve this improved operating characteristic while maintaining thetransconductance of the deflector system substantially unchanged or evensomewhat increased.

It is a corollary object of the invention to achieve these objectiveswith a structure adapted to mass production on an economical basis andwithout materially complicating the structure of known beam deflectiontubes.

The beam deflection tube constructed in accordance with the inventioncomprises means including a cathode for projecting a sheet-like electronbeam of substantially rectangular cross-section toward an outputelectrode system including at least two anodes. A pair ofelectrostatic-deflection electrodes are disposed between the beamprojecting means and the output electrode system, flanking the normal orundeflected path of the beam. The tube further comprises an acceleratingelectrode, spaced from the deflection-control electrodes by a distanceless than the spacing between the deflection-control elem trodes, in theform of a conductive plate having an elongated slot in register with thebeam, together with a screen grid, directly connected to theaccelerating electrode and including a plurality of spaced conductiveelements effectively covering the slot in the accelerating electrode, toprovide a screened aperture system which cooperates with thedeflection-control electrodes to form a projection lens for focusing theelectron beam on the output electrode system.

The features of the present invention which are believed to be novel areset forth with particularity inthe appended claims. The invention,together with further objects and advantages thereof, may best beunderstood,-.-

however, by reference to the following description taken in connectionwith the accompanying drawing, in the. several figures of which likereference numerals indicate.

like elements, and in which: 7

Figure 1 is a cross-sectional view of a novel beam defiection tubeconstructed in accordance with the invention; and

Figure 2 is a schematic circuit diagram of a system in,

which the tube of Figure 1 is particularly useful.

ln Figure l, a new and improved beam deflection tubeconstructed inaccordance with the present invention comprises an electron-emissivecathode 10 provided withan.

internal indirect heater element 11, a slotted focusing electrode 12,and an accelerating electrode 13 formed of,

a conductive plate and provided with a central aperture or slot 14opposite the emissive surface of cathode 10. Cathode 10, focusingelectrode 12, and accelerating electrode 13 constitute an electron gunfor projecting a sheet-like electron beam of substantially rectangularcross-section along a predetermined center plane 15 bisecting theaperture or slot 14 of accelerating electrode 13 and the emissive.surface of cathode 10. The tube further comprises an out-l put electrodesystem including a pair of anodes 16 and 17 preferably, although notessentially, disposed on opposite sides of the center plane 15 and in acommon transverse plane. Alternative output electrode systems, as forexample an apertured anode followed by a conductive plate for collectingelectrons passing through the aperture of the first anode, may beemployed, as is well known in the art. The tube also comprises a pair ofelectrostatic-deflection electrodes 18 and 19, flanking the tube centerplane 15 and disposed intermediate accelerating electrode 13 and outputelectrode system 16, 17. Deflectors 18 and 19 may advantageously beformed as simple parallel rods or wires, as illustrated in the drawing,or may comprise opposed deflection plates or the like as is well knownin the art, The tube may also advantageously comprise a box-likesuppressor electrode system 20 including a suppressor vane 21 extendingalong the center plane 15 between output anodes 16 and 17 in a mannerwhich is also well known in the art.

That portion of the tube thus far described may be of entirelyconventional construction. However, in accordance with the presentinvention, the tube further comprises a screen grid 22 constructed of aplurality of spaced conductive elements effectively covering slot 14 ofaccelerating electrode 13. Preferably, screen grid 22 is disposedintermediate accelerating electrode 13 and deflection-control electrodes18 and 19, although other constructions in which the screen grid isplaced in the plane of the accelerator slot or even closely adjacentslot 14 on the side of accelerator 13 facing focusing electrode 12 maybe employed. Screen grid 22 is preferably formed of a plurality ofspaced parallel wires extending in a direction transverse to the tubecenter plane 15 and eflectively covering aperture 14 of acceleratingelectrode 13 to form a screened aperture system which cooperates withdeflectors 18 and 19 to constitute a projection lens for focusing theelectron beam on or in the plane of output electrode system 16, 17. Thetube may also advantageously comprise a. second screen grid 23 betweendeflectors 18, 19 and output anodes 16, 17; screen grids 22 and 23 mayconveniently be formed as a single winding of continuous wire supportedby a pair of conventional grid support posts or wires 24, with thedeflectors 18 and 19 encompassed by the winding constituting screengrids 22. and 23. Preferably, the screen grid winding is formed in themanner illustrated-in the drawing, with the two efiective screen gridportions-22 and 23 of substantially planarconfiguration intersectingthebeam axis at right angles.

All of the electrodes have a substantial longitudinal extent in adirection perpendicularto the plane of the drawing to provide ahigh-currentsheetbeam. The entire electrode system may be mounted in anysuitable manner within a glass or metal envelope 25, which is thenevacuated and gettered in accordance with well known practices in theart.

In operation, when suitable-operating potentials are applied to therespective electrodes of the device of Figure 1, a sheet-like electronbeam of substantially rectangular cross-section is projected throughslot- 14 of accelerating electrode 13. Upon the application ofalternating signal voltages to electrostatic-deflection electrodes18-and 19, the beam is deflected'back and forth across the tube centerplane 15 to energize suitable load circuits associated with therespective anodes 16 and 17. In these more general aspects, theoperation of the tube of Figure 1 is entirely conventional.

Conventional beam deflection tubes, not provided with screen grid 22,have exhibited an undesirable tendency to draw excessive input deflectorcurrent in response to the application of large input signal voltages.This tendency is readily understandable when it is considered that, whenthe input signal amplitude is increased, the deflection amplitude mayalso be increased to the point where the electron beam grazes oractually impinges on the deflection-control electrodes. Thus, the inputdeflectors may draw beam current and produce an undesirable loadingeflect on the associated input circuit. In order to reduce this tendencyto draw deflector current, the spacing between the input deflectors maybe increased, to permit a larger deflection amplitude without causingthe beam to graze the deflection-control electrodes. However, inconventional beam deflection tubes, any'increase in the spacing betweenthe deflectors is necessarily accompanied by a decrease in thedeflection sensitivity and the input transconductance. More importantly,this expedient also results in a decrease in the positive bias potentialrequired for the deflectors to insure focus of the beam in the plane ofthe output electrode system. In practice, it has been found that inorder to accommodate input signal voltages of the magnitudeoftendesired, it has been necessary to increase the separation betweenthe deflectors to such an extent that the deflector potential requiredfor proper focusing drops to cathode potential or even lower. In such acase, it is no longer possible to employ directcurrent coupling from theoutput anodes of ,a preceding stage, which are normally maintained atpositive operating potentials.

When screen grid 22 is provided between accelerator 13 and deflectors18, 19, in accordance with the present invention, screen grid 22 andslotted accelerator 13 to gether constitute a screened aperture systemwhich cooperates with deflectors 18 and 19 to form a projection lens forfocusing the beam in the plane of the output system. Since theconductive elements of screen grid 22 intersect the center plane of thesheet beam at right angles, the only ripples or disturbances in theequipotential surface presented by the screen grid occur in a planetrans verse to that in which beam focus is required. The refractivepower of the electron lens constituted by the deflectors and thepreceding accelerating system is increased, and the bias potentialrequired to be applied to the deflectors to achieve focusing in theplane of the output electrode system, for a given deflector spacing, isalso increased in the positive direction. Consequently, the separationbetween the deflectors may be increased to a greater extent in order toreduce the tendency to draw excessive deflector current without causingthe deflector potential required for proper beam focus to be reducedbelowthe average potential of the output electrodes of a precedingstage. Moreover, it has been discovered that when screen grid 22 isprovided in accordance with the present invention, such increase in theseparation between the input deflectors not only entails no reduction indeflection sensitivity or input transconductance, but is actuallyaccompanied by-a small though noticeable increase in transconductance.

The second screen grid 23 and the suppressor system 20, -21- arepreferably included "to provide pentode-type operating characteristics.Second screen grid 23 provides a post-deflection accelerating fieldwhich is particularly' advantageous for the purpose of directing thedeflcted electrons to the output anode'on the same side of the centerplane 15 on which they leave the transverse deflection field establishedby deflectors 18 and 19 and for the additional purpose of furtherincreasing the positive deflector potential required for beam focus andfurther reducing the amount of beam current drawn by the deflectors,while the suppressor system 20, 21 prevents the generation of spuriousoutput signal components attributable to secondary electron emission.

The beam deflection tube of the present invention is particularly,although not exclusively, useful in a system of the type illustratedschematically in Figure 2, in which a pair of triode amplifiers 30 and31 are employed to provide a balanced input signal to a beam deflectiontube 32 of the type illustrated in Figure 1. The cathodes of triodes 30and 31 are connected to ground, and the anodes 33 and 34 are connectedto a suitable source of positive unidirectional operating potential,conventionally designated B+, through respective load resistors 35' and36. The control grids 37 and 38 of triodes 30 and 31 are returned toground through respective signal sources 39 and 40. In order to utilizeto advantage all of the beneficial attributes of the invention, signalsources 39 and 40 are preferably of the type having essentialdirectcurrent components and may constitute, for example, photosensitivecells whose outputs are to be compared.

Anodes 33 and 34 of triodes 30 and 31 are directly connectedtodeflectors 18 and 19 respectively of beam deflection tube 32. Cathode10, focusing electrode 12, and suppressor 21 may be directly connectedto ground, and accelerating electrode 13 and screen grids 22 and 23 maybe connected together and to B+. Anodes 16 and 17 are connected to B+through respective output resistors 4Laud 42. The use of the commonsymbol B-lto indicate positive operating potential connections is not tobe construed as requiring all connections so designated to be returnedto a single operating potential, but it is contemplated that thepositive operating potentials applied to the several points of thecircuit designated B-l 'may be of either the'same-or different values,depending on the requirements-of thercircuit.

In operation, respective single-ended signals having significantdirect-current components are applied from sources 39 and 40 to controlgrids 37 and 38 of mode closed in the'abovc-identified copendingapplicationsmay have the following characteristic dimensions:

amplifiers 30 and 31. As previously indicated, these sig- Inches nalsmay be derived from a pair of photosensitive cells Spacing from cathode10 to focusing electrode 12-- .005 the outputs of which are to becompared. If the illu- 5 Width of slot m focus ng electrode 12 .030mination of the two photocells is different, the average Spacing betweenfocusing electrode 12 and accelvoltage drops appearing across loadresistors 35 and 36 crating electrode 13 .056 are correspondinglydifierent, with the magnitude of the Width of slot 14 .030 differenceindicating the desired output diflerence read- Distance fromaccelerating electrode 13 to screen ing. The output voltages developedacross resistors 35 10 grid 22 .012 and 36 are applied to deflectors 18and 19 respectively Diameter of deflectors 18 and 19 .040 of beamdeflection tube 32 to establish a transverse de- Separation betweendeflectors 18 and 19-. .060 fiection field proportional to the voltagedifference be- Di tance from screen grid 22 to screen grid 23 .140 tweenanodes 33 and 34. The division of beam current Distance from screen grid23 to centers of deflectors between anodes 33 and 34 is proportioned tothe deflec- 15 18 and 19---- .113 tion field between deflectors 18 and19, and correspond- DiSiP-HCS from scffiin grid 23 10 anodes 16 and ingamPlified output voltages F acress All of the sheet metal electrodeswere constructed of put resistors 41 and 42. The deviation of either ofthese Stock and extended for a direction perpendicular voltages from theanode Source i may be to the plane of the drawing for a distance of 5inch. ployed as an indication of the desired difference read- 20 Screengrids 22 and 23 were wound as a single formed solenoidal winding of .004diameter wire having a pitch ,Through the 9 l of Screen gnd m accordanceof 32 turns per inch. The entire electrode assembly was with the presentf the sepfuatlon i deflectors mounted in a conventional miniature tubeenvelope be- 13 and 19 P be Increased 9 avmd 39 deflector tween a pairof mica spacers in a conventional manner. current whlle at sameretammgihe advan' 25 A tube constructed in this manner delivered a totalantages of P and balanced Opel-anon: More ode current of 12 milliamperesat an accelerating volt- Over the reducnon transconductance occaslonedby age of 250 volts, and exhibited the following transconthe increasedseparation between deflectors 18 and 19 ductances: required to avoidexcessive deflector current is smaller than the increase effected by theaddition of screen grid 220 mlcromhos at a deflector Potent"ll of 22, sothat a net increase in the input transconductance Volt? i achieved 320mrcromhos at a deflector D. C. potent al of +75 volts h i i f Figure 2 imflrely an illustrative 420 mrcromhos at a deflector D. C. potentialofvolts ample f one system in which a tube constructed in 270 rn'lcromhosat a deflector D. C. potential of 0 volts cordance with the inventionmay be employed and the 35 160 mlcromhos at a deflector D. C. potentialof 35 volts benefits and advantages of invention achiellcd- With abalanced A. C. voltage of 120 volts peak-to-peak ever, beam deflectiontubes constructed in accordance li to the d fl t 13 and voltage at leastwith the invention y also be p y t0 advantage four times in excess ofthe A. C. voltage required to as VideO amplifiers PW!er amplifiers intelevision effect complete transfer of the beam between anodes ceivefsor the like, in y Other circuit system 40 16 and 17the total D. C.current drawn by deflectors P y g m deflecfitm mbes- The invention is ofP 18 and 19 remained 5O microamperes or less throughiiculal' advantagein connection 'With the! new and out the range of D. C. deflectorpotentials from -35 proved beam deflection tubes and synchronizingcontrol lt to +150 1 systems described and claimed in one or more of theThus the invention provides a new and improved beam following copendingapplications: deflection tube affording the advantages of stable transInventor Serial No. Filing Date Title John G. Spmoklpn 246,768 September15, 1951...- Television Receiver.

259,063- November 30, 1951- 0.-.. Robert Adler.

263,737, 'now Patent 323,752, now Patent December 28, 1951--- 2 November17, 1952. November 17, 1952.

December 3, 1952 January 12, 1953 Do. Television Receiver ScanningSystem. Television Receiver.

In the systems described in the above-mentioned copending applications,a beam deflection tube is employed as an element in the feedback loop ofa scanning oscillator, with a large A. C. signal appearing between itsdeflectors and with automatic frequency control being effected byvarying the D. C. potential difference between the same deflectors inaccordance with the output voltage from a balanced phase detector. Thestable trausconductance over a wide range of D. C. deflector voltagesand the low beam current drawn by the deflectors, even at largepeak-to-peak input signals, achieved by the tube of the presentinvention are of especial advantage in connection with a system of thistype.

Merely by way of illustration and in no sense by way of limitation, abeam deflection tube constructed in acconductance over a wide range ofdirect voltage bias conditions for the input deflectors, low deflectorcurrent, and increased transccnductance and deflection sensitivity. Thetube is of general utility in any system in which the use of beamdeflection tubes is feasible, being of particular advantage inenvironments requiring or permitting balanced operation and/ordirect-current coupling.

While a particular embodiment of the present invention has been shownand described, it is apparent that various changes and modifications maybe made, and it is therefore contemplated in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

I claim:

1. An electron-discharge device of the beam-deflection cordance with theinvention for use in the systems distype comprising: an electron gunincluding an elongated apropos eteetron emissi'v'e cathode a a anaccelerating electrode having a naribwslot parallel to said cathode forprojecting along a predetermined center plane a sheetlike electron beamof snstantiauy rectangular cross-section; a pair of deflection=controlelectrodes flanking said center plane and spaced from each other by adistance greater than the spacing between said accelerating electrodeand said deflection-controlelectrodes; an output system including a pairof output electrodes; and a screen grid directly connected to saidaccelerating electrode and including a plurality of spaced conductiveelements effectively covering said slot to provide a screened aperturesystem which, together with said deflection-control electrodes,constitutes a projection lens for focusing said electron beam on saidoutput system.

2. An electron-discharge device of the bCalli-dCfiBCtiCn typecomprising: an electron gun including an elongated electron emissivecathode and an accelerating electrode having a narrow slot parallel tosaid cathode for projecting along a predetermined center plane asheetlike electron beam of substantially rectangular cross-section; apair of defiecti'on control electrodes flanking said center plane andspaced from each other by a distance greater than the spacing betweensaid accelerating electrode and said deflection'cont'rol electrodes; anoutput system including a pair'of output electrodes; and a screen grid,directly connected to said accelerating electrode and including aplurality of spaced conductive elements extending transversely acrosssaid center plane, interposed between said accelerating electrode andsaid deflection-control electrodes.

3. An electron-discharge device of the beam-deflection type comprising:an electron gun including an elongated electron-emissive cathode and anaccelerating electrode having a narrow slot parallel to said cathode forprojecting along a predetermined center plane a sheetlike electron beamof substantially rectangular cross-section; a pair of deflection-controlelectrodes flanking said center plane and spaced from each other by adistance greater than the spacing between said accelerating electrodeand said deflection-control electrodes; an output system including a'pair of output electrodes; a screen grid, directly connected to saidaccelerating electrode and including a plurality of conductive elementsextending transversely across said center plane, interposed between saidaccelerating electrode and said deflection-control electrodes; and asecond screen grid interposed between said deflectioncontrol electrodesand said output electrode system.

4. An electron-discharge device of the beam-deflection t'y'p'ecomprising: an electron :gun including an elongated electron-emissivecathode and an accelerating electrode havinga narrow 'sl'ot parallel tosaid cathode for project ing along a predetermined center plane asheetlike electron beam of substantially rectangular cross-section; apair of deflection-control electrodes flanking said center plane andspaced from each other by a distance greater than the spacing betweensaid accelerating electrode and said deflection-control electrodes; anoutput system including a pair of output electrodes; a screen grid,directly connected to said accelerating electrode and including aplurality of conductive elements extending transversely across saidcenter plane, interposed between said accelerating electrode and saiddeflection-control electrodes; and a second screen grid integral withsaid first screen grid and interposed between said deflection-controlelec' trodes and said output electrode system.

5. An electron-discharge device of the beam-deflection type comprising:an electron gun including an elongated electron-emissive cathode and anaccelerating electrode having a narrow slot parallel to said cathode forprojecting along a predetermined center plane a sheetlike electron beamof substantially rectangular cross-section; a pair of deflection-controlelectrodes flanking said center plane and spaced from each other by adistance greater than the spacing between said accelerating electrodeand said deflection-control electrodes; an output system'including apair of output electrodes; a screen grid, directly connected to saidaccelerating electrode and including a plurality of conductive elementsextending transversely across said center plane, interposed between saidaccelerating electrode and said deflection-control electrodes; a secondscreen grid integral with said first screen grid and interposed betweensaid deflection-control electrodes and said output electrode system; andmeans interposed between said second screen grid and said outputelectrode system for'suppressing secondary electron emission from saidoutput electrodes.

References Cited in the file of this patent

